dsh-premium-themes: DeepSeek Harness Premium Color Scheme Plugin

`dsh-premium-themes` is a standalone hot-swappable plugin for DeepSeek Harness (DSH) that adds advanced palette functionality to the Web interface. It introduces a "Color Scheme" option in General Settings, providing eight built-in schemes (such as Tokyo Night) and a custom import feature. It supports theme persistence, dynamic token mapping, and fine-grained JSON control, requires the `ui-theme` plugin to run, and allows users to quickly switch or customize the appearance without modifying core code.